A Lowpass Filter With Compact Size and Sharp Roll-Off

In this letter, a lowpass filter (LPF) is proposed based on a modified complementary split-ring resonator (CSRR) which can be considered as a traditional rectangular CSRR attached with two C-shaped structures, and a composite resonator composed of a simple uniform line with four stub-loaded stepped impedance resonators (SLSIRs) connected at the four corners. The LPF was designed using the first two resonant points produced by the composite resonator, and operating mechanisms are investigated based on its equivalent models. The LPF was fabricated and measured. The measured results are in good agreement with the full-wave simulated results, showing the merits of compact size and sharp roll-off.